Lebensraum (German: "living space") was Germany's term for its rapid conquests in the early 1940s. Hitler believed that the German Aryans deserved to be head of a vast empire. The Nazis specially felt they should conquer territory in the east, round Russia and neighbouring countries and settle German peasant farmers there.  At that time it meant in and round the USSR. The people dispossessed through this were considered Racially inferior (Jews, Gypsies, Slavs etc). Even in western countries like occupied France people considered inferior were dispossessed. Dispossessed people lost their property and were resettled in bad places. Later they were used as slave labour and worked to death or killed in Concentration camps.  That was known as the Holocaust.
Trying to conquer like that was risky, we know that because in the end Nazi Germans were defeated.